1. Field of the Invention
The present invention relates to methods and apparatus for aligning and trimming folded printed paper booklets commonly known as signatures, which are supplied in a continuous shingled, i.e. overlapping, stream from a preceding web press, combination folder or flow folding station.
2. Description of the Prior Art
Various arrangements have been heretofore proposed for aligning and trimming a continuous stream of shingled signatures. In general, these arrangements involve a series of smooth belts which hold the signatures between them as they move past a trimming station. These belts are driven by friction rollers and must be highly tensioned in order to grip the signatures and move them past the cutting wheels of the trimming station. However, when the signatures are flowing at a high rate of speed, such as 30,000 signatures per hour, and the preceding press or folding stations malfunctions, the signatures may bunch up and in attempting to pass through the trimmer will cause either one or more of the belts to break. In some instances, the belts in prior trimming apparatus have been broken twice in a single eight hour shift of operation. If the tension on these belts is reduced in an effort to reduce such breakage, the signatures are not held firmly as they pass by the cutting wheels and non parallel or uneven cuts are produced. Also, as the tension is reduced to avoid breakage the variation in cut registers increases due to movement of the signatures as they flow past the cutting wheels. With many prior art arrangements the variation in width is greater than .+-.1/8 of an inch, a condition which is accepted with great dissatisfaction in the industry.
A further disadvantage of prior art signature trimming apparatus in that this equipment usually trims each edge of the signature stream by passing if through opposed overlapping cutting wheels which trim the edge by a scissors type action. Since the edge of the signatures is not held against a surface while it is cut, there is difficulty in maintaining a straight cut and the trimmed edges may have an undesired ripple effect.
The stream of signatures from the printing press or folding station are usually considerably out of alignment. Accordingly, it is necessary to employ apparatus, commonly known as a jogger, to align the signatures before they are fed to the trimming apparatus. As stated heretofore, signatures consist of sheets of paper upon which images have been placed by a web press after which the sheets of paper are folded in half a number of times. One side of the final signature will contain nested folds and the side adjacent to it will have independent folds. When the folder makes a series of folds on a sheet of paper, air tends to become trapped within the folds and the folder is usually arranged to perforate the folds which are independent so that air can escape and the signature will lie flatter. The side wherein the folds are nested is called the spline and forms the back of the signature. At right angles to the spline are the independent folds which are perforated. The other two sides of the signature include loose sheets of paper, are never in alignment, and also lack rigidity. Accordingly, signatures are always aligned either against the spline or the side with the independent folds. However, when the top and bottom of the signature is trimmed, as in conventional two knife trimmers, the spline is positioned at right angles to the direction of flow and hence the signature can only be aligned against the independent fold side.
Conventional jogging apparatus employs a fixed slide plate on one side of the signature stream and a pivoted jogger plate on the other side which is pivoted back and forth so that it alternately slightly compresses the signature flow against the fixed slide plate and them releases the signature flow to provide a rough alignment of the overlapped signatures. Since the pivoted jogger plate strikes the edge of the signature stream at a slight angle it inherently creates disturbances within the signature flow and causes the signature to bounce back slightly from the fixed plate in random fashion. As a result, the best tolerance which can be achieved with this type of apparatus is only .+-.1/8 of an inch and this tolerance is oftentimes exceeded. If more precise alignment is desired it is customary to use a second similar jogging apparatus on which the pivoted jogger plate has a reduced swing and is moved back and forth more slowly so that it engages a signature a fewer number of times. However, the folded signatures may come out of different types of presses or folders with the independent fold side of the signature on either the inboard or the outboard side of the conveyor. This means that under some conditions the signatures will be aligned by pushing the loose sheet side of the signature against the fixed plate which results in relatively poor alignment even if two pivoted joggers are employed in series.